1 //===- FuzzerDFSan.cpp - DFSan-based fuzzer mutator -----------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 // DataFlowSanitizer (DFSan) is a tool for
10 // generalised dynamic data flow (taint) analysis:
11 // http://clang.llvm.org/docs/DataFlowSanitizer.html .
12 //
13 // This file implements a mutation algorithm based on taint
14 // analysis feedback from DFSan.
15 //
16 // The approach has some similarity to "Taint-based Directed Whitebox Fuzzing"
17 // by Vijay Ganesh & Tim Leek & Martin Rinard:
18 // http://dspace.mit.edu/openaccess-disseminate/1721.1/59320,
19 // but it uses a full blown LLVM IR taint analysis and separate instrumentation
20 // to analyze all of the "attack points" at once.
21 //
22 // Workflow:
23 // * lib/Fuzzer/Fuzzer*.cpp is compiled w/o any instrumentation.
24 // * The code under test is compiled with DFSan *and* with special extra hooks
25 // that are inserted before dfsan. Currently supported hooks:
26 // - __sanitizer_cov_trace_cmp: inserted before every ICMP instruction,
27 // receives the type, size and arguments of ICMP.
28 // * Every call to HOOK(a,b) is replaced by DFSan with
29 // __dfsw_HOOK(a, b, label(a), label(b)) so that __dfsw_HOOK
30 // gets all the taint labels for the arguments.
31 // * At the Fuzzer startup we assign a unique DFSan label
32 // to every byte of the input string (Fuzzer::CurrentUnit) so that for any
33 // chunk of data we know which input bytes it has derived from.
34 // * The __dfsw_* functions (implemented in this file) record the
35 // parameters (i.e. the application data and the corresponding taint labels)
36 // in a global state.
37 // * Fuzzer::MutateWithDFSan() tries to use the data recorded by __dfsw_*
38 // hooks to guide the fuzzing towards new application states.
39 // For example if 4 bytes of data that derive from input bytes {4,5,6,7}
40 // are compared with a constant 12345 and the comparison always yields
41 // the same result, we try to insert 12345, 12344, 12346 into bytes
42 // {4,5,6,7} of the next fuzzed inputs.
43 //
44 // This code does not function when DFSan is not linked in.
45 // Instead of using ifdefs and thus requiring a separate build of lib/Fuzzer
46 // we redeclare the dfsan_* interface functions as weak and check if they
47 // are nullptr before calling.
48 // If this approach proves to be useful we may add attribute(weak) to the
49 // dfsan declarations in dfsan_interface.h
50 //
51 // This module is in the "proof of concept" stage.
52 // It is capable of solving only the simplest puzzles
53 // like test/dfsan/DFSanSimpleCmpTest.cpp.
54 //===----------------------------------------------------------------------===//
55
56 /* Example of manual usage:
57 (
58 cd $LLVM/lib/Fuzzer/
59 clang -fPIC -c -g -O2 -std=c++11 Fuzzer*.cpp
60 clang++ -O0 -std=c++11 -fsanitize-coverage=3 \
61 -mllvm -sanitizer-coverage-experimental-trace-compares=1 \
62 -fsanitize=dataflow -fsanitize-blacklist=./dfsan_fuzzer_abi.list \
63 test/dfsan/DFSanSimpleCmpTest.cpp Fuzzer*.o
64 ./a.out
65 )
66 */
67
68 #include "FuzzerInternal.h"
69 #include <sanitizer/dfsan_interface.h>
70
71 #include <cstring>
72 #include <iostream>
73 #include <unordered_map>
74
75 extern "C" {
76 __attribute__((weak))
77 dfsan_label dfsan_create_label(const char *desc, void *userdata);
78 __attribute__((weak))
79 void dfsan_set_label(dfsan_label label, void *addr, size_t size);
80 __attribute__((weak))
81 void dfsan_add_label(dfsan_label label, void *addr, size_t size);
82 __attribute__((weak))
83 const struct dfsan_label_info *dfsan_get_label_info(dfsan_label label);
84 } // extern "C"
85
86 namespace {
87
88 // These values are copied from include/llvm/IR/InstrTypes.h.
89 // We do not include the LLVM headers here to remain independent.
90 // If these values ever change, an assertion in ComputeCmp will fail.
91 enum Predicate {
92 ICMP_EQ = 32, ///< equal
93 ICMP_NE = 33, ///< not equal
94 ICMP_UGT = 34, ///< unsigned greater than
95 ICMP_UGE = 35, ///< unsigned greater or equal
96 ICMP_ULT = 36, ///< unsigned less than
97 ICMP_ULE = 37, ///< unsigned less or equal
98 ICMP_SGT = 38, ///< signed greater than
99 ICMP_SGE = 39, ///< signed greater or equal
100 ICMP_SLT = 40, ///< signed less than
101 ICMP_SLE = 41, ///< signed less or equal
102 };
103
104 template <class U, class S>
ComputeCmp(size_t CmpType,U Arg1,U Arg2)105 bool ComputeCmp(size_t CmpType, U Arg1, U Arg2) {
106 switch(CmpType) {
107 case ICMP_EQ : return Arg1 == Arg2;
108 case ICMP_NE : return Arg1 != Arg2;
109 case ICMP_UGT: return Arg1 > Arg2;
110 case ICMP_UGE: return Arg1 >= Arg2;
111 case ICMP_ULT: return Arg1 < Arg2;
112 case ICMP_ULE: return Arg1 <= Arg2;
113 case ICMP_SGT: return (S)Arg1 > (S)Arg2;
114 case ICMP_SGE: return (S)Arg1 >= (S)Arg2;
115 case ICMP_SLT: return (S)Arg1 < (S)Arg2;
116 case ICMP_SLE: return (S)Arg1 <= (S)Arg2;
117 default: assert(0 && "unsupported CmpType");
118 }
119 return false;
120 }
121
ComputeCmp(size_t CmpSize,size_t CmpType,uint64_t Arg1,uint64_t Arg2)122 static bool ComputeCmp(size_t CmpSize, size_t CmpType, uint64_t Arg1,
123 uint64_t Arg2) {
124 if (CmpSize == 8) return ComputeCmp<uint64_t, int64_t>(CmpType, Arg1, Arg2);
125 if (CmpSize == 4) return ComputeCmp<uint32_t, int32_t>(CmpType, Arg1, Arg2);
126 if (CmpSize == 2) return ComputeCmp<uint16_t, int16_t>(CmpType, Arg1, Arg2);
127 if (CmpSize == 1) return ComputeCmp<uint8_t, int8_t>(CmpType, Arg1, Arg2);
128 assert(0 && "unsupported type size");
129 return true;
130 }
131
132 // As a simplification we use the range of input bytes instead of a set of input
133 // bytes.
134 struct LabelRange {
135 uint16_t Beg, End; // Range is [Beg, End), thus Beg==End is an empty range.
136
LabelRange__anon144c25d90111::LabelRange137 LabelRange(uint16_t Beg = 0, uint16_t End = 0) : Beg(Beg), End(End) {}
138
Join__anon144c25d90111::LabelRange139 static LabelRange Join(LabelRange LR1, LabelRange LR2) {
140 if (LR1.Beg == LR1.End) return LR2;
141 if (LR2.Beg == LR2.End) return LR1;
142 return {std::min(LR1.Beg, LR2.Beg), std::max(LR1.End, LR2.End)};
143 }
Join__anon144c25d90111::LabelRange144 LabelRange &Join(LabelRange LR) {
145 return *this = Join(*this, LR);
146 }
Singleton__anon144c25d90111::LabelRange147 static LabelRange Singleton(const dfsan_label_info *LI) {
148 uint16_t Idx = (uint16_t)(uintptr_t)LI->userdata;
149 assert(Idx > 0);
150 return {(uint16_t)(Idx - 1), Idx};
151 }
152 };
153
operator <<(std::ostream & os,const LabelRange & LR)154 std::ostream &operator<<(std::ostream &os, const LabelRange &LR) {
155 return os << "[" << LR.Beg << "," << LR.End << ")";
156 }
157
158 class DFSanState {
159 public:
DFSanState(const fuzzer::Fuzzer::FuzzingOptions & Options)160 DFSanState(const fuzzer::Fuzzer::FuzzingOptions &Options)
161 : Options(Options) {}
162
163 struct CmpSiteInfo {
164 size_t ResCounters[2] = {0, 0};
165 size_t CmpSize = 0;
166 LabelRange LR;
167 std::unordered_map<uint64_t, size_t> CountedConstants;
168 };
169
170 LabelRange GetLabelRange(dfsan_label L);
171 void DFSanCmpCallback(uintptr_t PC, size_t CmpSize, size_t CmpType,
172 uint64_t Arg1, uint64_t Arg2, dfsan_label L1,
173 dfsan_label L2);
174 bool Mutate(fuzzer::Unit *U);
175
176 private:
177 std::unordered_map<uintptr_t, CmpSiteInfo> PcToCmpSiteInfoMap;
178 LabelRange LabelRanges[1 << (sizeof(dfsan_label) * 8)] = {};
179 const fuzzer::Fuzzer::FuzzingOptions &Options;
180 };
181
GetLabelRange(dfsan_label L)182 LabelRange DFSanState::GetLabelRange(dfsan_label L) {
183 LabelRange &LR = LabelRanges[L];
184 if (LR.Beg < LR.End || L == 0)
185 return LR;
186 const dfsan_label_info *LI = dfsan_get_label_info(L);
187 if (LI->l1 || LI->l2)
188 return LR = LabelRange::Join(GetLabelRange(LI->l1), GetLabelRange(LI->l2));
189 return LR = LabelRange::Singleton(LI);
190 }
191
DFSanCmpCallback(uintptr_t PC,size_t CmpSize,size_t CmpType,uint64_t Arg1,uint64_t Arg2,dfsan_label L1,dfsan_label L2)192 void DFSanState::DFSanCmpCallback(uintptr_t PC, size_t CmpSize, size_t CmpType,
193 uint64_t Arg1, uint64_t Arg2, dfsan_label L1,
194 dfsan_label L2) {
195 if (L1 == 0 && L2 == 0)
196 return; // Not actionable.
197 if (L1 != 0 && L2 != 0)
198 return; // Probably still actionable.
199 bool Res = ComputeCmp(CmpSize, CmpType, Arg1, Arg2);
200 CmpSiteInfo &CSI = PcToCmpSiteInfoMap[PC];
201 CSI.CmpSize = CmpSize;
202 CSI.LR.Join(GetLabelRange(L1)).Join(GetLabelRange(L2));
203 if (!L1) CSI.CountedConstants[Arg1]++;
204 if (!L2) CSI.CountedConstants[Arg2]++;
205 size_t Counter = CSI.ResCounters[Res]++;
206
207 if (Options.Verbosity >= 2 &&
208 (Counter & (Counter - 1)) == 0 &&
209 CSI.ResCounters[!Res] == 0)
210 std::cerr << "DFSAN:"
211 << " PC " << std::hex << PC << std::dec
212 << " S " << CmpSize
213 << " T " << CmpType
214 << " A1 " << Arg1 << " A2 " << Arg2 << " R " << Res
215 << " L" << L1 << GetLabelRange(L1)
216 << " L" << L2 << GetLabelRange(L2)
217 << " LR " << CSI.LR
218 << "\n";
219 }
220
Mutate(fuzzer::Unit * U)221 bool DFSanState::Mutate(fuzzer::Unit *U) {
222 for (auto &PCToCmp : PcToCmpSiteInfoMap) {
223 auto &CSI = PCToCmp.second;
224 if (CSI.ResCounters[0] * CSI.ResCounters[1] != 0) continue;
225 if (CSI.ResCounters[0] + CSI.ResCounters[1] < 1000) continue;
226 if (CSI.CountedConstants.size() != 1) continue;
227 uintptr_t C = CSI.CountedConstants.begin()->first;
228 if (U->size() >= CSI.CmpSize) {
229 size_t RangeSize = CSI.LR.End - CSI.LR.Beg;
230 size_t Idx = CSI.LR.Beg + rand() % RangeSize;
231 if (Idx + CSI.CmpSize > U->size()) continue;
232 C += rand() % 5 - 2;
233 memcpy(U->data() + Idx, &C, CSI.CmpSize);
234 return true;
235 }
236 }
237 return false;
238 }
239
240 static DFSanState *DFSan;
241
242 } // namespace
243
244 namespace fuzzer {
245
MutateWithDFSan(Unit * U)246 bool Fuzzer::MutateWithDFSan(Unit *U) {
247 if (!&dfsan_create_label || !DFSan) return false;
248 return DFSan->Mutate(U);
249 }
250
InitializeDFSan()251 void Fuzzer::InitializeDFSan() {
252 if (!&dfsan_create_label || !Options.UseDFSan) return;
253 DFSan = new DFSanState(Options);
254 CurrentUnit.resize(Options.MaxLen);
255 for (size_t i = 0; i < static_cast<size_t>(Options.MaxLen); i++) {
256 dfsan_label L = dfsan_create_label("input", (void*)(i + 1));
257 // We assume that no one else has called dfsan_create_label before.
258 assert(L == i + 1);
259 dfsan_set_label(L, &CurrentUnit[i], 1);
260 }
261 }
262
263 } // namespace fuzzer
264
265 extern "C" {
__dfsw___sanitizer_cov_trace_cmp(uint64_t SizeAndType,uint64_t Arg1,uint64_t Arg2,dfsan_label L0,dfsan_label L1,dfsan_label L2)266 void __dfsw___sanitizer_cov_trace_cmp(uint64_t SizeAndType, uint64_t Arg1,
267 uint64_t Arg2, dfsan_label L0,
268 dfsan_label L1, dfsan_label L2) {
269 assert(L0 == 0);
270 uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
271 uint64_t CmpSize = (SizeAndType >> 32) / 8;
272 uint64_t Type = (SizeAndType << 32) >> 32;
273 DFSan->DFSanCmpCallback(PC, CmpSize, Type, Arg1, Arg2, L1, L2);
274 }
275 } // extern "C"
276